Diaphragm pumps possess many advantages and are widely used. When a reciprocating drive is used for a diaphragm pump, a dished diaphragm can be used to accommodate linear reciprocating motion. As its name implies, a dished diaphragm has a dished section in the form of a frustum of a right circular cone to accommodate the reciprocating motion.
A nutating or wobble plate drive can also be used to drive a diaphragm pump, and one such construction is shown in my U.S. Pat. No. 4,153,391. Although a wobble plate drive provides a type of back and forth motion, it is quite different from linear reciprocation.
A conventional dished diaphragm is not suitable for use with a wobble plate drive. When they are used together, volumetric efficiency decreases, and diaphragm wear increases. This is caused by the fact that the nutating motion is larger at radial outer regions of the diaphragm than at radial inner regions of the diaphragm. Accordingly, the dished section at the radial inner regions of the driven portion of the diaphragm is too large and is free to be drawn into the pumping chamber on the intake stroke to reduce the volume of the pumping chamber and is forced in the other direction on the discharge stroke. The repeated flexing of the diaphragm in this manner accelerates wear on the diaphragm, and bulging of the diaphragm into the pumping chamber on the intake stroke reduces the volumetric efficiency.
There are a variety of wobble plate drives for diaphragm pumps as shown by my U.S. Pat. Nos. 4,153,391 and 4,396,357. Although these wobble plate drives function satisfactorily, production problems can arise due to a build up of tolerances from the various parts of the drive.
As shown by my U.S. Pat. No. 4,153,391, it is common practice to provide a separate output valve for each of the pumping chambers of a diaphragm pump. Although separate outlet valves function satisfactorily, they increase the cost of the pump somewhat, and this is significant in the crowded and highly developed pumping field.